Super cell 'lurking' as Sydney cops 4600 lightning strikes

SYDNEYSIDERS were rudely woken from their slumber at 4am today as a deafening thunderstorm ripped through the city.

One user on social media site Reddit summed it up: "The first massive crack of thunder was literally the loudest I have heard in my life. I physically jumped in the air, and my heart is still pounding."

But meteorologists have scoffed at the storm's strength saying it "wasn't even severe". And they've warned a far more dangerous super cell storm could be lurking in its wake.

Meanwhile, in Western Australia, the Bureau of Meteorology (BoM) has said there is now a "significant risk" of a cyclone forming over the coming days.

More than 4600 lightning strikes hit Sydney early this morning with electricity providers working to restore power to thousands of homes.

A still from the Bureau of Meteorology radar at around 6am showing the storm that passed over Sydney.

Super cells are caused when wind shear reaches high levels leading the storms to rotate. These storms can be violent and are often accompanied by strong winds and hail. However conditions can change quickly which could see the super cell fail to develop.

BoM has not yet issued a severe thunderstorm warning for Tuesday for NSW.

Nevertheless, it has said storms are likely in Sydney on Tuesday with a high of 31C and up to 20mm of rain. In the city's west, the mercury could reach as high as 37C.

Cooler conditions in NSW had been forecast for this afternoon but Chiari said that might now be delayed.

"The cool change is coming through but later than initially forecast. It's looking more like the evening around 6pm or 7pm."

In the Kimberley region of Western Australia, a tropical low is building up strength that could see it become a tropical cyclone.

A large storm seen passing over Sydney on Monday afternoon. Picture: Ian Gilchrist

The low has made landfall and is currently tracking towards Derby and Broome.

The BoM said the low is bringing sustained winds with gusts of up to 85km/h. It should move off land on Tuesday but could well come back in a different form.

"The low is expected to strengthen over open water and may become a tropical cyclone on Wednesday or Thursday," the BoM said.

"There is a significant risk of a severe tropical cyclone impacting northern WA later in the week."

Elsewhere conditions are calmer. Melbourne will have a sunny day and a high of 22C rising to 34C by Thursday. It's set to be a balmy 32C in Brisbane while Darwin will be 33C and stormy.

Further south, Adelaide will reach 26C on a sunny day with a high of 35C on Thursday. Hobart will be 22C with possible showers while Perth will reach 35C.